# Guide Essentials of Radio Wave Propagation

The radio horizon is the locus of points at which direct rays from an antenna are tangential to the surface of the Earth.

## Long Distance Propagation of HF Radio Waves

If the Earth were a perfect sphere without an atmosphere, the radio horizon would be a circle. The radio horizon of the transmitting and receiving antennas can be added together to increase the effective communication range. Radio wave propagation is affected by atmospheric conditions, ionospheric absorption , and the presence of obstructions, for example mountains or trees. Simple formulas that include the effect of the atmosphere give the range as:. The simple formulas give a best-case approximation of the maximum propagation distance, but are not sufficient to estimate the quality of service at any location. Earth bulge is a term used in telecommunications. It refers to the circular segment of earth profile that blocks off long distance communications.

Radio Wave Propagation in Antennas and Wave Propagation by Engineering Funda

Since the geometric line of sight passes at varying heights over the Earth, the propagating radio wave encounters slightly different propagation conditions over the path. Assuming a perfect sphere with no terrain irregularity, the distance to the horizon from a high altitude transmitter i.

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Let R be the radius of the Earth and h be the altitude of a telecommunication station. The line of sight distance d of this station is given by the Pythagorean theorem ;. If the height is given in metres, and distance in kilometres, .

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The above analysis does not consider the effect of atmosphere on the propagation path of RF signals. Thus, the maximum service range of the station is not equal to the line of sight geometric distance. Usually, a factor k is used in the equation above, modified to be. But in stormy weather, k may decrease to cause fading in transmission. That is equivalent to a hypothetical decrease in Earth radius and an increase of Earth bulge.